What is Sound Damping?

Damping removes vibration energy from a structure or system by eliminating the dynamic stresses associated with vibration. Installing appropriate sound damping measures ultimately adds to the wear or fatigue life of structural or machine components.

What is Sound Absorption?

When sound waves strike any surface, some of those waves pass through the material and others reflect or bounce off of the surface. Materials with a harder, less porous surface tend to produce a higher level of reflection, while porous materials allow for greater absorption.

Liz, Author at Technicon Acoustics

Author Archives: Liz

A Closer Look at Sound Damping vs. Absorption
September 30, 2019 12:14 pm Leave a Comment
Acoustic vibration or acoustic energy—more commonly referred to as noise—can be mitigated or eliminated using sound damping or sound absorption techniques. Damping reduces acoustic vibration within any type of structure, wall, or system. In contrast, sound absorption works to dissipate airborne acoustic energy or sound waves. Though different, both achieve the same goal of mitigating unwanted noise.

What is Sound Damping?

Damping removes vibration energy from a structure or system by eliminating the dynamic stresses associated with vibration. Installing appropriate sound damping measures ultimately adds to the wear or fatigue life of structural or machine components.

A greater understanding of the damping function requires a closer examination of how vibration works:
- Vibration travels through different materials at varying levels of intensity. When vibration frequency is equivalent or similar to the natural frequency of a material, it results in amplification.
- Frequency amplification makes vibrations harsher, more jarring, or louder.
- Applying damping materials to substrates that amplify vibrations alters the resonating frequency, reducing the impact of vibration on the system and its components.
The level of damping provided by each type of damping material relates to the material’s damping coefficient. The damping coefficient measures the material’s capacity to produce “bounce back”—or return energy to a system or structure. Materials with lower damping coefficients produce higher bounce back, while those with a higher damping coefficient reduce unwanted vibration or shock by soaking up the vibrational energy. Of note, this process produces a small amount of heat.

Common materials used in damping usually include viscoelastic materials, such as PVC and constrained layer foam composites.

What is Sound Absorption?

When sound waves strike any surface, some of those waves pass through the material and others reflect or bounce off of the surface. Materials with a harder, less porous surface tend to produce a higher level of reflection, while porous materials allow for greater absorption. Acoustic absorption uses porous materials to line hard surfaces that typically reflect sound or airborne noises, such as those produced by:
- Heavy machinery
- Engines
- Power tools
- Generators
Sound absorbers contain porous materials like foam or blended fiber that keep sound waves from reflecting back into open spaces. Lining harder materials with absorbers like polyester fiber, polyester foam, or polyether foam reduces ambient noise produced by sound reflection.

Applications of Acoustic Components for Enhanced Performance

Technicon uses a variety of sound absorbing and sound damping materials to mitigate acoustic vibration and noise in a broad range of applications. Our acoustic foam—often referred to as sound absorbing foam or soundproofing foam—is available in a variety of thicknesses and facing configurations for both functionality and aesthetic purposes.

These products will reduce ambient noise in applications such as:
- Machine enclosures (generators, air compressors, water pumps, etc.)
- Engine compartments
- Truck and heavy equipment cabs
- Home appliances
- Medical equipment
We also provide sound damping materials. Application of our vibration damping composites control vibration fatigue and structure-borne noise, often in combination with sound absorbers to reduce airborne noise as well.

Let Our Acoustic Specialists Help You

Whether your specific application requires a reduction in acoustic vibration through sound damping or noise reduction provided by sound absorption, Technicon Acoustics has the solution. We are a leading producer of both acoustic and thermal solutions for a broad range of original equipment manufacturers (OEMs) throughout North America.

Contact us or request a quote to learn more about the sound damping and sound absorption solutions available from Technicon.
The (not so) Silent Threat to American Classrooms
March 13, 2019 4:10 pm Leave a Comment
The (not so) Silent Threat to American Classrooms and ways to address it.

Noise is everywhere. Unless it’s a movie or naptime, you can’t really find a quiet place inside a school. Especially, the place where quiet should matter the most; the classroom.

The impact that noise has on classrooms can be easily overlooked. You don’t think about the hmm of the air conditioner or the rattle of the pipes, but experts believe that students miss up to 33 percent of learning material because they can’t understand what’s being said. Children who are especially sensitive; socio-emotional or those whom have learning, or behavioral challenges for example are more susceptible to the impacts of noise. Not the mention the teachers who suffer from vocal strain trying to talk over the noise.

The National Heart Association says chronic noise can cause elevated stress responses in the human brain. This is especially straining for students because unlike adults, children haven’t developed the ability to interpret meaning from words that they don’t fully understand.

Noise pollution from outside noise, HVAC units, the humming of lights can have serious health and cause performance impacts on students. For example, an air conditioner found in Decatur, GA aka “the beast” is a staggering 60 decibels. Schools do take the performance of their districts seriously. However, noise inside of the classroom is not a priority. To reduce noise levels and bring awareness to noise issues in schools the American National Standards Institute in 2002 published a set of standards to be used by designers, school planners, and school districts that dictates maximum noise and reverberation levels in classrooms. (ANSI_S2.60) Keep in mind that this, however is not a requirement. It is recommended that decibels levels in schools not exceed 35 decibels. It has been recorded by researchers that noise classroom can reach between 66 to 94 decibels! In a TED Talk by sound expert Julian Treasure, he makes it clear that Architects need to use their ears as well as their eyes. Here are some solutions to show you how.

Solutions

Keep in mind

Sound is lazy and will always take the easiest path to get from point A to B. The easiest path for sound to travel is a clear unobstructed path. If you can visually see the noisy machine, there is nothing obstructing or reducing the noise from the maximum amount that you can receive. It is important to not only place something in-between and the noisy machine but also to make sure that there is no place for the noise to slip through the holes and cracks.

Structure Borne vs Air Borne Noise

Structure Borne noise is cause by vibration the different components. The vibration can cause structures as well or sheet metal to resonate. Initial design can control a large portion of this problem. The preferred method of controlling residual structure-borne noise is to isolate the cause of the vibration.

Air Borne Noise can be reduced through proper design elements and acoustical treatments. The primary consideration in design to reduce Air Borne Noise is to make sure that all air paths in or out of the enclosure are tortuous and to ensure that all large flat sound reflecting surface are treated with appropriate soft sound absorbing materials.

Know the causes

Heating and cooling systems play a major part in excessive classroom noise because to save dollars, schools often place HVAC units in each classroom instead of a centralized system. Individual units typically are nosier. Another reason for the excess noise is the lack of Acoustic Standard being applied to building codes in the same fashion as lighting and ventilation. Ensuring that equipment used in and around classrooms is manufactured to the quietest possible standards is the easiest way to reduce unwanted noise in the classroom.
Double Belt Lamination Technicon Acoustics
February 20, 2019 7:14 pm Leave a Comment
Technicon Acoustics adds double-belt lamination capabilities

Dual Belt Laminator

At Technicon, we continue to invest in the latest manufacturing technologies to ensure we can make high quality materials as effectively as possible. Our newest equipment is a new double belt lamination process. This line has independent heat zones on the top and bottom as well as infrared heating on the in-feed side of the machine. This gives us the ability to laminate multi-layer materials in one pass as well as the ability to laminate new materials that will expand our product line.
- PF-091
- Tech Shield ™
Technicon Acoustics, located in Concord, NC is the leading manufacturer in Acoustic and Thermal solutions for OEM’s across North America. We design, develop, and deliver parts and materials that absorb, block and isolate sound and thermal energy.

For more information about our Acoustic and Thermal fabrication capabilities, please visit our capabilities page.
5 things to know about Die Cutting
October 29, 2018 6:51 pm Leave a Comment
5 things to know about Die Cutting

More cutting methods are available now than ever before. In the early days, Friction Sawing used to be the “go-to” material cutting option. Now, there are literally dozens of choices. In this blog, we’re going to focus on Die Cutting and determine if it’s right for you.

What is Die Cutting?

According to Wikipedia, Die Cutting is “the general process of using a die to shear webs of low-strength materials, such as rubber, fiber, foil, cloth, paper, corrugated fiberboard, paperboard, plastics, pressure-sensitive adhesive taps, foam and sheet metal”. Die cutting provides versatility in fabrication and allows us to make custom parts, like gaskets across a variety of applications and are perfect for providing high volume precision cutting.

1.) Benefits of Flatbed Die Cutting

First, there’s Rotary Die Cutting and Flatbed die cutting. Flatbed Die Cutting is the process of cutting or perforating the desired shape our of material using a hydraulic press. Flatbed cutting reduces overall cost and used generally for large production runs, higher cutting efficiency, high part consistency. The Flatbed cutting process allows quick change over times from one part to another which increases overall efficiency.

2.) Common Applications
- Acoustical Insulation
- Appliances
- Compressors
- Generators
- Heavy Equipment
- Marine
- Medical Equipment
- Power Tools
- Tractor
- Truck Body and Cab
To see the industries we serve, click here: //www.techniconacoustics.com/industries/

3.) Die Cutting is perfect for custom kits

Die Cutting allows customed engineered designs to be cut into one large piece with perforated cuts, with each individual part separately labeled. This allows for quicker receiving and an overall simplified inventory process. Kitting makes assembly workers more efficient and increases output helping you reduce labor costs.

Worried about Quality and re-work? At Technicon, for the previous 12 months, our quality performance was 99.98%. See the //www.techniconacoustics.com/company-about-us/the-perfect-order/

4.) Puts the “Lean” in Lean Manufacturing

Die Cutting reduces Material wastes and costs, time set up, loss and decreases parts. The more parts the less the efficiency.
1. Saves on Storage Space
2. Just In time delivery- get what you need exactly when you need it
3. Get custom packaging
5.) Die Cut Gaskets

Are reliable, customizable, and cost-effective. Die cut gaskets can be produced on rotary or flatbed equipment that helps reduce overall cost. At Technicon, we have a multiple point checklist in the production process. Pre- Production Planning or (PPP) can cut costs to make sure that everything is examined and in order from the time of the RFQ to purchasing and packaging. Die cutting allows us to give you design flexibility, low set up cost and supply chain flexibility.
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Absorbers vs Barriers
October 25, 2018 5:31 pm Leave a Comment
When you’re not really sure what solution you’re looking for you usually search for “soundproofing”. We receive calls that sound like “how do you make this oxygen air compressor quiet?” Or Is there a way to soundproof my office?

People are convinced that soundproofing foam, sound absorbing foam or soundproofing panels are the “cure all”. Well, doesn’t foam stop sound? No. Foam doesn’t “stop” sound. It absorbs echo. This is a common misconception that follows confusion when OEM’s and everyday people are looking for sound solutions for their next project. Let us help you understand the difference and which one is best for your next project.

What is an Absorber?

First, let’s determine what an Absorber does. Sound absorbers are porous materials used to line hard sound-reflective surfaces to reduce airborne noise. Airborne noise is a sound that is transmitted through the air, typically generated by
- Speech
- Television and Radio
- Animal Sounds
- Transport
In construction, you typically find structure-borne noise which is transmitted through a solid structure, such as steel, wood, concrete stone etc. Once the sound strikes the material, the sound energy is dissipated as heat. Typical absorbers used are acoustical foams and fibers. At Technicon Acoustics we produce absorbers that are acoustical foams and fibers for both functional and aesthetic purposes with a wide variety of foam or non-woven absorbing materials. Common examples of sound absorbers are open cell foam and polyester fibers. To determine the amount of material necessary to reduce the noise, our engineering team uses our Acoustics Lab to ensure there are no gaps, cracks or leaks to allow sound to escape from the enclosure.

Common Uses of Sound Absorbers

• Machine enclosures

• Generator, air compressor, & water pump enclosures

• Engine compartments

• Truck & heavy equipment cabs

• Home appliances

• Medical equipment

Click here for the technical

specification for an Absorber.

What is a Barrier?

Barriers (soundwall, noise wall) are slightly different than absorbers because they are used to block noise transmitting from one location to another. A Sound Barrier is a Mass Loaded Vinyl (MLV) used to reduce the amount of airborne sound transmitting through a wall,

floors, ceilings etc.

While Barriers are heavy as lead, they usually aren’t that thick. This allows the MLV to improve Sound Transmission Loss without taking up space; like at a Construction Site. Barriers can be wrapped or be used with other material like our Thermal Solution Product Tech Shield.

*Keep in mind, that noise can be absorbed by sound absorbers or blocked by a barrier. We can also reduce structure-borne noise that causes vibrations using our Damping Material. *

Common Uses for Sound Barriers

• Machine enclosures

• Engine compartments

• Firewalls

• Bulkheads

• Cab floors

• Pipe Wrap

To view, our case studies and additional applications go to www.techniconacoustics.com or if you just have more questions. Click to request a chat with the Sales Team.
Tech Shield ™ Knowledge Guide
5:06 pm Leave a Comment

Protect Components from Damaging Heat

Technicon Acoustics TECH SHIELD ™ TS-040 is designed to shield components from radiant heat sources. Made from a flexible and lightweight inorganic core that is naturally flame retardant and thermally insulating, our new TECH SHIELD ™ offers a noticeable drop in “cold side” or “body side” temperatures allowing for improved comfort inside cabins and operator environments. The high performance PSA offers quick and easy installation to a wide variety of surfaces.

High Heat Protection

Applications

Tech Shield is ideal for applications in Heavy Equipment, Specialty Vehicles, Power Generation, Appliances, Heavy Truck, and Automotive Industries.
- Firewall & Underbody
- Exhust & Turbo Trouble Areas
- Hose & Tubing Protection
- HVAC Thermal Protection
- Fuel Tank Shielding
How to design and plan for Acoustics
4:46 pm Leave a Comment
Benefits during the initial design

There are new methods and processes that are constantly changing the game for designers. Partially the reasoning for this problem is the ever-growing challenges designers face every day.

Development Speed: Constant Revision and parts not being efficient or poor quality

Complexity Management: If the project is overly complex, usability and budget can be difficult. This increases risk and chances of error.

Customer Involvement: Keeping potential customers involved is tricky. Questions are needed to get the appropriate feedback that will help move the project forward.

Sustainability: You can have a killer design idea, but either the products aren’t sustainable on either an economic or environmental level. Costs are too high for large quantity production not to mention recyclable or minimizing the use of materials ensures good global citizenship.

So first, keeping all the challenges in mind how do you not only address key product design issues, but design to reduce noise and more importantly manage cost? Well, let’s look at the benefits of providing a Sound Solutioned Environment.

An environment that provides reduced noise levels increases efficiency and improves output and can minimize hearing loss claims. In a classroom, It can increase learning capabilities and clear speech. According to the United States General Accounting Office “21,900 schools exhibit poor acoustics or noise control, affecting over 11 million students. 28.1% of all schools reported unsatisfactory or very unsatisfactory environmental noise conditions. This was higher than ventilation (27.1%), physical security (24.2%), indoor air quality (19.2%), heating (18.9%), or lighting (15.6%)” Reducing noise in the workplace can have health benefits by reducing Cardiovascular Disease and Workplace distractions.Global Analytics writes ” Businesses lose about $600 Billion Dollars a year in workplace distractions” You get the picture. Basically, NOT designing for noise can be expensive. So let’s look at the different types of noise, how to discover acoustical mistakes BEFORE they are made, and important key design elements to consider.

Air Borne or Structure Borne

What is Airborne Noise? Airborne Noise is a condition when sound waves are being carried by the atmosphere. Examples are Engine Noise, Turbo Whine, and Fan Noise…Structure-borne Noise is Mechanical Vibration in a structure which can become an audible sound. Example: Mounted Devices, Sheet Metal Structures, and Body Panels.

Airborne noise can be reduced through proper design elements and acoustical treatments. The primary consideration in design to reduce airborne noise is to make sure that all air paths, in or out of the enclosure are tortuous. This eliminates the line of sight noise transmission. Another design consideration is to ensure that all doors and access panels are properly fitted and gasketed to provide a complete seal. As little as 10% untreated surface areas will reduce the effectiveness of acoustical treatments by up to 50%. All interior surfaces of the enclosure should be treated using the proper acoustical absorber or absorber/barrier composite.

Structure-borne noise can be reduced by considering the nature of the structure-borne sound which can vary significantly depending on the source of the vibration, the composition of the structure through which it will transmit. The radiating surface and the character of the receiving space.

Key Design Issues

When looking at using the right products you should know that there is no such thing as one right material for all applications. For example, Barrier composites only need to be used between noise sources and OCCUPIED areas. Absorber products are less expensive, lighter and will make a major impact that will fill gaps and voids. More is not always better. If there is more than 5% untreated area, don’t waste money by adding mass. Something that happens quite often is the absorber is often covered. Covering the Absorber negates its purpose. There are other ways to get the look you want like with different facing combinations so it’s important to consider the environment and know the frequency. All acoustic products have a signature. We can help you pick the right one for your application

Key Take Away’s
- Treat as close to the source as possible
- Block the Noise Paths
- Leave room for treatment
- Use the right products
Treat at the source, Block the path, and Plan for materials

Treat at the source
- When you treat close to the source of the noise; if can you treat smaller areas and you eliminate secondary effects. For example, soft engine mounts to isolation engine vibration and stop structure-borne noise. Soft mount gensets, inverters, and other equipment. Use sound shields/enclosures around equipment where possible.
Block the noise paths.
- Structure Borne noise will travel along all rigid hard connections until it finds a sympathetic surface to radiate sound. To solve this problem, you can introduce isolation barriers where practical. Airborne noise will follow all air paths and reflect off all hard surfaces. Here, you can make sure all air paths are either sealed or “tortuous”. You can line as much surface area as possible with sound absorbers or absorber/barrier composites.
Plan for Acoustic Materials
- Be sure to leave space for treatment. Minimize equipment attached directly to bulkhead adjacent to occupied areas by either stand-off the attachments or attempt to make attachments on the outboard or other non-occupied bulkheads. Be sure to leave room between hulls, bulkheads and other structures for the application of sound absorbers and composites. We would typically recommend a 3″ recommended clearance.
Common myths

There’s is no such thing as 1 material for all applications.

– Barrier composites only need to be used between noise sources and OCCUPIED areas. You can also use absorber product because it’s cheaper and lighter and will make a major impact in reducing noise if you fill all the gaps and voids.

More is not always better.

-Too much over-engineering has been done in the past. If there is more than 5% untreated area, don’t waste money adding mass.

Keep these rules in mind:

1.) Don’t cover the absorber
- Covering the absorber negates its purpose. There are other ways to get the look you want.
2.) Find the right mounts
- Many equipment manufacturers do not do the work required to provide the best vibration isolation mounts.
3.) Consider the environment
- If the product will be exposed to heat, water, diesel, gas, etc make sure it’s going to stand up.
4.) Know the frequency

All acoustic products have a signature. Pick the right
The Cost of Noise
September 17, 2018 7:58 pm Leave a Comment
On average the CDC reports that in 2007, “82% of the cases involving occupational hearing loss were reported among workers in the manufacturing sector” Hearing Loss is the most commonly recorded occupational illness in Manufacturing accounting for 1 in 9 recordable illnesses. It’s estimated, that there are 16 million people working in the Manufacturing Sector, which accounts for approx 13% if the US workforce.

Hearing loss disability results in an estimated $242 million dollars worth of workers compensation payments each year. According to hear-it.org. As many as 95% of construction workers are exposed to high levels of noise on a daily basis. When left untreated, hearing loss can reduce earnings by as much as $30,000 a year. The top industries that have the most hearing loss claims? Construction, Carpentry, Farmers, and Mining resulting in 30 million work-related injuries each year. The machines that caused the most noise are Jackhammers, Dump trucks, Cement Mixers, Electric Saws. Plant work and Power Stations resulted in 100 DBA ( A-weighted decibels) with Sewer water and Residential Construction sites following behind between 93-99 DBA. *see how to measure noise on a construction site*

Most will argue that the primary cause for the hearing loss injuries in Manufacturing, Construction, Mining etc is that there’s a lack of educational training on how to prevent Occupational Hearing Loss. According to Mr. Neitzel’s report:

“Occupational health regulations governing the construction industry, including those pertaining to hearing conservation, are generally less comprehensive than those for the general industry. As a result, health surveillance and prevention programs for chronic diseases such as NIHL are limited in the industry. The US Occupational Safety and Health Administration (OSHA) has two regulations pertaining to hearing conservation in the construction industry. The first… set forth an eight-hour time-weighted average (TWA) permissible exposure limit of 90 dB, and requires a hearing conservation program (HCP) for workers whose exposures exceed this level. The second, [regulation] requires the use of hearing protection devices (HPDs) when noise exposures cannot be reduced below the Permissible Hearing Levels PEL.”

Source: healthyhearing.com

See the Story on how poor acoustics affects farmers Source: National Geographic

How to solve it

Marine

Whatever kind of boat you build, your customers will appreciate your efforts to make it quieter. Engine noise, prop cavitations, shaft whirl, all generate noise and create a vibration that can be controlled with the right noise control materials. Here’s our recommendation for a 47″ Trawler Yacht.
- Engine Room – Use Absorber/Barrier composites. The absorber layer reduces reverberant noise. The barrier layer reduces sound transmission from the engine compartment.
- Bulkheads – Here, you can also use an absorber and barrier. Either separately or in a composite to reduce reverberant noise and block sound.
- Hull Structure – Treat hull and deck vibration with proper damping materials.
How to measure reverberant noise

Transportation

Operators of Transportation products such as trucks, buses, trains and emergency vehicles spend their entire day in the vehicle. The major noise sources in a vehicle are the engine, accessories, road and wind noise. Noise can enter the operator and passenger compartments by a variety of paths – through the glass, dash, floor doors etc.
- Flooring Systems – Road Noise is generated by the vehicles passage over the highway surface and resulting tire and air noise. By using a Barrier Composite you can reduce the impact of road noise on the operator and its passengers.
- Body Panels – Large surfaces such as floor pans and door panels are prone to vibration. Typically, the greater the surface the greater the noise. Vibration damping materials applied to these surfaces reduce vibration – radiated noise.
- Hood Liners -These can be manufactured to act both sound absorbers and Heat Shields. They can reduce the reverberant engine noise thus improving both the outdoor environment and the cab interior. They can be made with a protective, heat-resistant facing and sound-absorbent material.
Heavy Equipment

Major noise sources in heavy equipment are the engine, drive train and power take-off systems. The sound radiates throughout the environment and affects operators, bystanders, nearby businesses and individuals.

Read the blog: Tuning into Urban Noise
- Operator’s Cab- Headliners and sidewall trim systems that incorporate sound absorbers and sound barriers can be used to block sound entering the operator’s compartment and absorb sound reflection from within the operator’s cab. (Contact us to see which facings can be used for functional and aesthetic purposes.
- Firewall and floormat systems- Firewall composites block sound from the engine and drive train and prevent noise from entering the cab. These can be manufactured either with or without a heat shield component. Sound barriers bounded to a durable wear surface create floormats that reduce sound transmission and improve operator comfort.
Technicon Acoustics did a case study on measuring and decreasing noise in the cab of a motor grader. Click here to see the results

Contact Us

See our list of Solutions and Capabilities at www.techniconacoustics.com and request a consultation with our Sound Solution Sales Team.
Our Favorite TED Talks about Sound and Noise
7:57 pm Leave a Comment
Harnessing the power of sound

Humans are wired for sound. Steve Keller, one of the world’s leading experts in the field of audio branding, explores how brands are harnessing the power of sound and music to shape our perception and influence our behavior, ultimately asking the question: How can we use these same strategies and
tactics to make our world a better place?

The 4 ways sound affects us

Playing sound effects both pleasant and awful, Julian Treasure shows how sound affects us in four significant ways. Listen carefully for a shocking fact about noisy open-plan offices.

Tinnitus Ringing of the Brain

In this talk, Josef Rauschecker illuminates the science behind tinnitus as well as the current state of treatment options.

SShhh! Sound Health In 8 Steps

Julian Treasure says our increasingly noisy world is gnawing away at our mental health — even costing lives. He lays out an 8-step plan to soften this sonic assault (starting with those cheap earbuds) and restore our relationship with sound.

Why Architects need to use their ears

Because of poor acoustics, students in classrooms miss 50 percent of what their teachers say and patients in hospitals have trouble sleeping because they continually feel stressed. Julian Treasure sounds a call to action for designers to pay attention to the “invisible architecture” of sound.

What are some of your favorite Ted Talks?

Technicon Acoustics

704.707.0421 | sales@techniconacoustics.com| 4412 Republic Court, Concord, NC 28027
Introduction to Acoustics
7:56 pm Leave a Comment
Absorption

Have you walked into a racquetball court and heard the echo as the ball strikes the wall? Or have you been in the country with snow on the ground and noticed how quiet it is. The difference in the sound between these to places is due to the degree that sound is absorbed. In the case of the racquetball court, the noise of the ball striking the wall travels to another wall and bounces off of it, travels to another wall and bounces off of it and so on. The echo is caused by the sound continually whizzing past your ear due to reflecting off another wall. In the case of being in a field with snow, your voice either continues to propagate down the field never striking anything, or strikes the snow and disappears. Whether a sound when striking an object reflects back or disappears is due to the objects sound absorption. The racquetball court typically is made of concrete painted walls. Concrete painted walls have very low sound absorption and hence, reflect. Five inches of fluffy snow, however, absorbs the sound when it strikes it.

Some materials allow sound to easily enter it. These materials are called porous. Acoustic porous materials can have a porosity greater than 90%. Porosity is the amount of volume that is just air. Common sound absorption materials are open cell foam and polyester fiber. Sound absorption is an energy conversion process. The kinetic energy of the sound (air) is converted to heat energy when the sound strikes the cells or fibers. Hence, the sound disappears after striking the material due to its conversion into heat.

We know that most sounds contain many different pitches or frequencies. A bass guitar plays low- frequency sounds while a violin plays high-frequency sounds. Low-frequency sounds have long wavelengths and high-frequency sounds have short wavelengths. A wavelength can be visualized when going to a beach. The wavelength is the distance from one wave crest to the next wave crest. In the air, a long wavelength propagates in all directions easily. That is why a single subwoofer is typically needed to fill a listening space due to the fact that subwoofers are not directional in nature. In contrast, a tweeter that emits high-frequency sounds is very directional. Reproduction of high-frequency sounds requires at least two carefully placed tweeters to produce a good stereo image of the sound. Low- frequency sound passes through materials much easier than high-frequency sounds. That’s why one can hear the constant thud of a subwoofer through the wall of the room next door. Because sound passes through materials differently at different frequencies, the sound absorption will typically change with frequency. Besides the sound absorption changing with frequency, it also changes with the thickness of the material. For the same materials, thin sections will not absorb as much low-frequency sound as will thicker pieces. Figure 1 provides absorption curves for the same material at three different thickness. The ordinate (left vertical axis) contains the absorption (alpha). The absorption can go from 0 (no absorption) to 1 (all sound is absorbed). The abscissa (horizontal axis) provides the frequency at which the absorption was measured.

1 – Figure 1. Affect of thickness on absorption

One may be wondering how sound absorption is measured. There are two main methods, one use a special room called a reverberation room and the other uses a special tube called an impedance tube. The reverberation room allows the sound to strike the material from all directions and hence is called random incidence. The impedance tubes have the sound strike the material straight on and are called normal incidence. Table 1 compares the two methods.

2 – Table 1. Comparison between Random Incidence and Normal Incidence Absorption

The Technicon impedance tube is shown below in figure 2:

Figure 2. Impedance Tube for Sound Absorption

The impedance tube consists of a speaker, tube, two microphones and material sample holder. A special sound called white noise is generated in the speaker. The white noise is composed of sound contributions from all frequency bands in the audible range. The sound travels straight down the tube and strikes the material. Some of the sound is absorbed and some are reflected back. The two microphones measure the reflected sound. From the two microphone’s signals, the sound absorption can be calculated.

From figure 1, one sees that one way of increasing the low-frequency absorption is by using a thicker material. Absorption of a non-faced porous material is called resistive. Placing a film on the surface of the material can increase the low-frequency absorption. This type of absorption is called reactive. Figure 3 compares non-faced foam with foam with an aluminized polyester face.

3 – Figure 3. Faced versus non-faced foam for same thickness

Figure 3 shows typical changes when placing a film or facing on the top surface of a porous material. The change in the sound absorption for the faced material is an increase at the lower frequency absorption and a decrease in absorption at the higher frequencies. This is due to the film now acting as a spring-mass resonator for the low-frequency peak. At the higher frequencies, the face causes the sound to reflect. Knowing how different faces can change the absorption of a material, Technicon can design the best sound absorber for our customer’s noise problem.

Sound Transmission Loss

The second technique to reduce noise is sound transmission loss. Sound Transmission Loss is abbreviated as STL. As the name sound transmission loss implies sound is blocked from transmitting through one space to another. For example, a wall in a movie theater separating one theater from the other requires high sound transmission loss to keep from hearing the gunfire, explosions, and crashes from the adjacent theater’s action movie.

There are a variety of ways of producing sound transmission loss. One way is distance. We all know that noisy machines are louder at close distances versus when farther away. When designing a school, for example, distance plays a good common sense noise control solution many times. A poor school design would place a gymnasium or cafeteria next to a library. However, in regards to machinery, distance, as a noise control solution is rarely practical.

Sound is lazy and hence will always take the easiest path to get from point A to point B. The easiest path for sound to travel is a clear unobstructed path. If you can visually see the noisy machine, there is nothing obstructing or reducing the noise from the maximum amount that you could receive. Hence, it is important not to only place something in between you and the noisy machine, but also to make sure that there is no place for that sneaky noise to slip through holes and cracks. A solution for blocking the noise from getting to you would be to place the machine in an enclosure. A well-designed enclosure will always make sound work hard to get to your ears; hence its essential to not have any holes, gaps or cracks. If ventilation is required for combustion intake and exhaust or cooling purposes, a sound silencer or labyrinth is necessary. The labyrinth lined with sound absorptive material forces the sound to strike the sound absorptive material hence causing the sound to be reduced significantly by the time it exists.

Now that the enclosure is pretty well sealed, sound can still reach you by transmitting through the enclosure walls. This is called airborne sound transmission. There are ways of increasing this sound transmission loss. The first is mass. Mass can be increased by using a thicker wall of the same material or use a more dense material. There is a relationship between sound transmission loss and weight of the barrier and this is called the mass law. The mass law states that for every doubling of the weight of the material, one can expect a 6 dB increase in the transmission loss. In addition to the mass having an effect on the transmission loss, the frequency of the sound also has a similar effect. A doubling of the frequency will create a 6-dB increase in the transmission loss. Figure 4 shows the effect of mass and frequency on sound transmission loss.

4 – Figure 4. Mass and Frequency dependence on Transmission Loss

One sees that the cost and weight of the wall must double for each 6 dB incremental improvement in transmission loss. If there are two walls and they are separated by a significant distance, each wall transmission loss is additive. This additive effect is shown in figure 5.

5 – Figure 5. Comparison between double and single wall for same total weight.

One can see from figure 5 that by adding a second wall and large air gap between the walls, the transmission loss can be dramatically increased. Double wall construction is encountered in many everyday systems. For example, in homes, drywall, stud construction is made of two sheets of drywall separated by the studs.

In the real world, the air gap between walls will be relatively small. In machinery enclosures, the gap may range from 1/4″ to 2″. The greater the gap, the more the walls behave as two separate walls instead of a single wall comprising of both walls total weight. In real-world double wall systems, a double wall resonance in the airspace occurs which reduces the transmission loss. To reduce the detrimental effect of the double wall resonance, a foam or fiber is placed in the air gap between walls. Technicon offers a variety of barrier composites. Barrier composites create a double wall system when attached to the interior wall of a machinery enclosure.

Vibration Damping

Many time’s large panels vibrate. The cause of vibration may be an engine, generator, compressor, road irregularities in vehicles or a boat hull slapping against the waves. When this occurs, the panel vibrates as a large speaker cone creating noise. This type of noise is called structural borne noise. The greater the panels move, the more air is displaced, the louder the sound. The vibration creates resonance in the panel causing it to move. Resonance is a natural phenomenon that can cause a mechanical structure to vibrate violently if the panel is excited at the same frequency that a resonance occurs. To keep a panel from resonating violently, the panel must be damped. Steel or fiberglass panels by themselves are stiff and elastic, causing them to vibrate a long time when struck. Hence, steel and fiberglass have very little damping. Hence, to damp the panels to reduce resonant vibrations, damping must be applied to the surface of the panels. Damping materials can be applied as a trawled on a compound or as sheets with an adhesive backing. The key feature of a damping material is that they are viscoelastic. Viscoelastic materials require energy to be extended and compressed. This is exactly where we want the vibration energy from the panels to go, into the viscoelastic materials and then dissipated as heat.

The amount of damping necessary to effectively reduce the panel vibrations is dependent on the panel thickness and material type. If one overdamps the panel, this adds extra cost and weight, hence, there is an optimal amount of damping for a given panel material and thickness. There are test standards to measure the damping loss factor of the damping material. The test standard performed at Technicon is ASTM E756. A picture of the test fixture for measuring the damping loss factor is given in figure 6.

Figure 6. Damping Test Rig with Sample

The damping test rig consists of a bar made from the panel material with the damping material bonded to it. Like the impedance tube, a white noise signal is fed to a vibration exciter at the top of the bar. This causes the bar to resonate. At the bottom of the bar, a vibration pickup measures the bar’s resonance. The transfer function is defined as the output vibration response of the bar divided by the input vibration excitation is calculated. This is shown in figure 7.

6 – Figure 7. Transfer Function of Damping Bar

The peaks in figure 7 are excited resonance in the bar. The broader the resonance peaks, the greater the damping. The composite damping loss factor is calculated by the formula:

Composite Loss Factor = [fh(-3 dB)- fl(-3 dB)]/fr

Where:

fr = Frequency at resonant peak

fh(-3 dB) = Higher Frequency at -3 dB below resonant peak

fl(-3 dB) = Low Frequency at -3 dB below resonant peak.

7 – Acoustics Lab for Reverberation Testing

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